Semiconductor devices such as logic and memory devices are typically fabricated by a sequence of processing steps applied to a specimen. The various features and multiple structural levels of the semiconductor devices are formed by these processing steps. For example, lithography among others is one semiconductor fabrication process that involves generating a pattern on a semiconductor wafer. Additional examples of semiconductor fabrication processes include, but are not limited to, chemical-mechanical polishing, etch, deposition, and ion implantation. Multiple semiconductor devices may be fabricated on a single semiconductor wafer and then separated into individual semiconductor devices.
Metrology processes are used at various steps during a semiconductor manufacturing process to detect defects on wafers to promote higher yield. Optical metrology techniques offer the potential for high throughput measurement without the risk of sample destruction. A number of optical metrology based techniques including scatterometry and reflectometry implementations and associated analysis algorithms are commonly used to characterize critical dimensions, film thicknesses, composition and other parameters of nanoscale structures.
In one example, two-dimensional beam profile reflectometers (2D-BPR) systems are employed to perform measurements of semiconductor samples. However, existing 2D-BPR systems acquire measurement signals one wavelength at a time. This limits the throughput of such systems when multiple illumination wavelengths are needed to accurately characterize the sample.
In another example, spectroscopic ellipsometry (SE) systems perform simultaneous measurements across a broad spectrum of illumination wavelengths. However, existing SE systems acquire measurement signals at one angle of incidence (AOI) at a time. This limits the throughput of such system when multiple AOIs are required to accurately characterize the sample.
In another example, optically based measurements of overlay targets are performed by overlay metrology tools manufactured by KLA-Tencor, Inc., using scatterometry overlay (SCOL) technology. Existing tools acquire SCOL signals one wavelength per acquisition. A control system is employed to change the illumination wavelength at each different acquisition. Exemplary tools employ multiple diode laser light sources or tunable laser light sources to provide illumination light at different, selectable wavelengths.
In yet another example, optically based measurements of overlay targets are performed by overlay metrology tools manufactured by ASML Holding NV. In some of these tools, a control system is employed to change the illumination wavelength at each different acquisition by selecting optical filters in the beam path at each acquisition.
In these examples, reflectance measurements of an overlay target are separately acquired at each wavelength. This sequential approach to data acquisition increases the time required to acquire data at multiple wavelengths and generate measurement recipes. Furthermore, the illumination system must be configured to provide illumination light at different, selectable wavelengths, which increases system complexity.
Metrology applications involving the measurement of overlay targets present challenges due to increasingly small resolution requirements and throughput requirements. Thus, methods and systems for improved overlay measurements are desired.